Expandable polystyrene beads

ABSTRACT

A styrene polymer bead impregnated with a blowing agent containing from about 0.5 to about 20 weight percent of an impregnation aid and the process for preparing same.

United States Patent 1 4 Taub et a1.

[ EXPANDABLE POLYSTYRENE BEADS [75] Inventors: Bernard Taub, Williamsville; Daniel F. Hamish, Orchard Park, both of NY.

[73] Assignee: Allied Chemical Corporation, New

York, NY.

[22] Filed: Dec. 17, 1973 [2 I] Appl. No.: 425,372

[ 1 Aug. 19, 1975 Moody et all 0. 26(1 3.344.221 /2.5 E Banks et al i. 260/25 B Primary LlmminerMorton Foelak Atlumqu Agent, or Firm-Michael L. Dunn; Jay P. Friedenson [57] ABSTRACT A styrene polymer bead impregnated with a blowing agent containing from about 0.5 to about 20 weight percent of an impregnation aid and the process for preparing samev 16 Claims, No Drawings EXPAN DABLE POLYSTY REN Ii HEADS BACKGROUND OF THE INVENTlOlw' Field of the Invention This invention relates to a process for the manulac ture of foamable thermoplastic resins. More particularly. this invention is concerned with a process for impregnating polystyrene beads with a liquid blim ing agent to produce foamable beads.

b. History of the Prior Art Foamable beads containing blowing agents are used in the production of rigid polymer foams. The blowing agents used have boiling points below the softening temperature of the thermoplastic beads and also exert very little solvent action on the beads. When the foam able beads are heated. the blowing agent aporizes causing the beads to expand to many times their original size. The foamed beads are then easily molded into a variety of useful articles such as cups. dishes. packaging materials, refrigerator components. insulation boards and the like.

There are several processes available for impregnating polystyrene beads with blowing agent. One process involves the aqueous suspension polymeriration of styrene in the presence of blowing agent. Another process involves treating polystyrene beads with blowing agent in aqueous suspension. Both of these processes require an aqueous diluent along with suspension stabilizers to insure sufficient incorporation of blowing agent into the polystyrene beads Other prior art processes disclose the use of gaseous hydrocarbon to impregnate the polystyrene beads. However. unduly long periods of time are required for impregnation. Another process uses liquifcd hydrocar bons to impregnate the polystyrene. However, the lat' ter process requires slightly elevated temperatures which can result in the agglomeration or fusion of the polystyrene beads.

BRIEF DESCRIPTION OF THE INVENTION The invention is a novel expandable styrene polymer particle and novel process for making same comprising contacting particles of the styrene polymer with a blow ing agent, said blowing agent containing from about tl.5 to about 20 and preferably from about 3 to about weight percent of an impregnation aid consisting of a compound having a solubility parameter between about 7 and I2 hildcbrands. a critical volume of less than about 190 cur /gram mole and a hydrogen bond ing parameter contribution to said solubility parametcr of less than 5 hildebrands The novel process as described herein permits int pregnation of polystyrene particles. e.g., polystyrene beads. with liquid blowing agents at low tem 'ieraturcs, e.g., between about and about C while preventing agglomeration of the particles. l he resulting particles are free flowing and readily expand upon ll'lt' appli cation of sufficient heat.

DETAILED DESCRIPTION OF THE INVENTION Styrene polymer as used herein means a polymer formed from at least weight percent and preferably at least weight percent styrene monomerv l he most preferred styrene polymer is formed from at least weight percent styrene monomer. Styrene monomer includes both methyl styrene and unsubstituted styrene but is preferably unsubstituted styrene (ill The styrene polymer particles are preferably polystyrene beads but may be particles of any shape. The size of tlic ptirtit lcs is generally between about l5 and about 'lfi mesh and is preferably between about It) and about 45 mesh.

The blowing agent is a volatile organic fluid which is :1 gas or which will produce gas upon heating. Preferred blowing agents include aliphatic hydrocarbons contain ing from I to 7 carbon atoms in the molecule and their halogenated derivatives which boil below the softening point of the styrene polymer but which preferably are not solvents for the polymer and do not readily escape from the polymer at room temperature. Examples of preferred hydrocarbon blowing agents are butane. isobutane. pcntanc. isopentane. n-hc\ane, 2-mcthyl pentanc and .l-ntcthyI pentane. Examples of preferred halogenated hydrocarbons are symmetrical and assymetiical dichlorotetrafluortiethanc and dichloroditluoromethane. Preferably from about 4 to about ll) weight percent blowing agent. including impregnation aid. is incorporated into the polymer.

The impregnation aid. which is incorporated into the blowing agent. is a compound which enhances the impregnation rate of a primary blowing agent into the styren polymer. The impregnation aid is a compound having a solubility parameter bctwccn about 7 and I2 hildcbrands. a critical volume of less than about IJU cnr gram mole and a hydrogen bonding parameter contribution to the solubility parameter of less than 5 ltiltlcbrands. The impregnation aid is believed to soften the styrene polymer thus permitting the blowing agent to be more easily incorporated into the styrene polymer. In order to soften the styrene polymer, the imregnation aid should have a solubility parameter close to the solubility parameter of polystyrene, icl, between about 7 and I2 hiltlebrands If a compound has a solubility parameter below about 7 or above about 12 l'lildebrands it will not act as an impregnation aid for polystyrene since the desired softening of the polystyrene will not occurv The solubility parameter unit is the square root of calories per cubic centimeter and is designated as a parameters as used herein are measured at 25 Cti'itl grade. The solubility parameter 5 may be broken di. vn

where 0,, is the dispersion component of the so ibility parameter. 5; is the polar component of the solubility parameter, and 6,, is the hydrogen bonding component oftbc solubility parameter. For a discussion of the solubility parameter see page 889 of the supplemental vol note of the Encyclopedia of('hcmical Technology Ind lid. Kirlcflthmer. published by John Wiley and Sons lire. New York 1971.

In order to insure the proper softening effect upon the styrene polymer by the impregnation aid. it has been found that the hydrogen bonding component of the solubility parameter should be less than 5 lnldclirunds.

in addition in order to insure proper penetration of on: impregnation aid into the styrene polymer it has also been found that the critical volume of the impregnation aid should be less than about 190 cm lgram rnt'vle. While not wishing to be bound by any particular lbw nv II is believed that the molecular size of the inn nildebrand. Unless otherwise indicated the solubility pregnation aid must be kept small in order to penetrate into the styrene polymer and that the low critical vol ume is related to the required small molecular size.

From about l to about 20 weight percent and prefer- The most preferred impregnation aid is (H- C" in that fusion and agglomeration of the heads seems to be less likely.

ln practicing the process of this invention the blowing ably from about 3 to about weight percent of im- 5 agent containing the impregnation aid is contacted with pregnation aid is incorporated into the blowing agent the styrene polymer particles, e.g., polystyrene beads, to assist penetration of the blowing agent into the styby any suitable means known to those skilled in the art. rene polymer. Before the present invention many blow- For example the styrene polymer particles may be ing agents either could not be incorporated by impregtacted with the blowing agent in liquid suspension or nation into the styrene polymer or could be incorpo- It) the particles may be contacted with the vapor of the rated only after extended periods of time or with the blowing agentv The process may be practiced at atmoapplication of heat. The addition of the impregnation spheric or superatmospheric pressures cg. 5 atmoaid reduces the time required for impregnation, permits spheres. The temperature at which the process is perthe use of blowing agents which could not previously be formed may vary but to reduce the likelihood of agused, and permits more rapid impregnation at lower l5 glomeration is preferably carried out near room temtemperaturcs than was previously possible. The maxiperature e.g., between about and 35 centigrade. mum amount of impregnation aid used is limited by the The following examples serve to illustrate the process softening effect of the impregnation aid upon the styof the invention whereby the novel impregnated styrene polymer. since th am unt f i p eg ti d rene polymer particles are formed. Unless otherwise used must be less than an amount which will cause un- 20 indicated a" parts d parcemuges are b i h acce table softenin Onl sufficient im re nation aid p I EXAMPLES is used to permit incorporation of the blowing agent into the styrene polymer particle to form a novel free In the following examples 200 grams of polystyrene flowing styrene polymer particle which will expand beads having an average particle size of between about upon application of sufficient heat to soften the styrene 20 and 45 mesh are added to an autoclave fitted with polymer. an agitator and cooling means. The autoclave is then Examples of suitable impregnation aids, their solubilevacuated and cooled and 500 grams of liquid blowing ity parameters, their hydrogen bonding contribution to agent, which may or may not contain impregnation aid, their solubility parameter and their critical volumes are are added. The mixture is then agitated for 6 hours at shown in table l. room temperature (25C), allowing the pressure to build up to the normal vapor pressure of the blowing TABLE I agent. After 18 hours the remaining liquid blowing a nti rmovdandt Compound Solubility Hydrogen Bonding Critical 88 S e he polystyrene beads are "1.6a

par-mum m m vo|um sured for blowing agent content and pre-puif density. The reuff densit is determined b measurin the h! 901 t 1m p y y g a'szz g sagat bead density after the beads are exposed to live steam ((HJJIFI at 95C for 5 minutes. The following table II for each 2-3 example, gives the blowing agent used, the impregnaf tion aid used, if any, the percent blowing agent absorpacetonitrile l 1.9 3.4 Z 40 tion, the weight ratio of blowing agent to impregnation i U aid. the pre-putf density in pounds per cubic foot if measured, and pertinent remarks.

TABLE ll Example Blowing lmpregnation Ratio Percent Pre-Pufl' Remarks on Resulting Agent Aid Absorption Density Beads 1. None IOU/(I (L8 No expansion 1 (HZCIF 95/5 I51 L7H Free flowing 3. ('HQCIF 93/7 l8. l.o7 Free flowing J. H 1( |F Ill/ll) 20.0 |.Ull Slight agglomeration S. LHZCIF 85/15 Fused h. LH;,('l L)7/3 no l5 Free flowing 7. CHHCI /5 I l.2 Free flowing K. (H;,(l 13/7 in K I .-ll Slight agglomeration 9. (H30 )l l/ l l) Fused ltl. ('H F )(l/ It) 1.4 Free flowing l l. ('HFLICHH )ll/ ll) LR Free flowing l2. Methyl l-onnate )7/3 2.8 Free flowing l3. Methyl Formate 4/! 7.4 Agglomeration l4. Methyl Form-ate )ll/lll Fused 15, CS: 97/3 9. Free flowing l 0. ('52 t Ill Agglomcration l7. (("l h Aeetonitrile 97/3 8.8 Free flowing l8. lsohutane None lUtl/U (Lo No expansion I). lsohutane CHQCIF JO/1U (1.4 2.0 Free flowing Ill. lsobutaiie (H-:CIF 5/ l 5 l(l.3 (Lhl Free flowing I l. lsohutaiie H;,(l JO/1U (1.1) LS4 Free flowing 22. lsobutane (H,.Cl l 5 ltth 0.49 Agglomeration 3. Pentane None IOU/ll (Lo No expansion 24-. Pentane (H-:(IF 5/5 I l .3 Slight agglomeration 25. Pcntane (H Cl 97/3 7.0 Agglomcmti 2b. lcnlane (H m 15/5 Fusion 27. lsopelitane None lUtI/l) it: No expansion TABLE II Continued liuimplc Blowing impregnation Ratio Percent lre-PutT Remarks on Resulting Agent Aid Absorption Dcnsit Beads 3H lsopcntanc ('H CI 97p. (\ll Slight agglomeration l Isopentanc ('H Cl 15. A Fusion 33. Butane None loom 3 o 2.5

33. Butane ('H fll 5/5 1.8 (H47 Free flowing 34 Butane (H1 )7/3 5.2 H Slight agglomeration 3 5. Butane (H (I Ii/5 H. 3 (L78 Agglomcration A comparison of the foregoing examples clearly indicates that when an impregnation aid as described herein is used in conjunction with a blowing agent better absorption of the blowing agent into the polystyrene results.

What is claimed is:

l. A process for making expandable styrene polymer particles by contacting particles of said styrene polymer with a volatile organic fluid blowing agent. said blowing agent containing from about 0.5 to about percent by weight of blowing agent of an impregnation aid consisting essentially of a compound having a solubility parameter between 7 and 12 hildebrands, a critical volume of less than about 190 cm/gram mole and a hydrogen bonding parameter contribution to said solubility parameter of less than 5 hildebrands, the impregnation aid being present in an amount sufficient to permit incorporation of the blowing agent into the styrene polymer particle to form a free flowing styrene polymer particle.

2. The process of claim 1 wherein the styrene polymer is insoluble in the blowing agent.

3. The process of claim 2 wherein said styrene polymer is contacted with the blowing agent in liquid suspension.

4. The process of claim 1 wherein the impregnation aid is selected from methyl chloride or monochloromonofluoromethane.

5. The process of claim 4 wherein the blowing agent is a hydrocarbon selected from butane, isobutane, pentane, isopentane, n-hexane, 2 methyl pentane and 5 methyl pentane.

6. The process of claim 4 wherein the blowing agent is a halogenated hydrocarbon selected from symmetrical and assymetrical dichlorotetrafluoroethane and dichlorodifluoromethane.

7. The process of claim 2 wherein the impregnation aid is monochloromonofluoromethane.

8. The process of claim 7 wherein said styrene polymer is contacted with the blowing agent in liquid suspension.

9. The process of claim 6 wherein the impregnation aid is selected from methyl chloride or monochloromonofluoromethane.

N). The process of claim I wherein the process is performed at a temperature between about 20 and about 35C.

11. The process of claim 1 wherein from about 3 to about 15 weight percent of impregnation aid is used.

12. A free flowing styrene polymer particle impregnated with a blowing agent containing from about 0.5 to about 20 percent by weight of blowing agent of an impregnation aid said impregnation aid consisting essentially of a compound having a solubility parameter between 7 and i2 hildebrands. a critical volume of less than about I em /gram mole and a hydrogen bonding parameter contribution to said solubility parameter of less than 5 hildebrands.

l3. The polymer according to claim [2 wherein the blowing agent is a hydrocarbon selected from butane, isobutane, pentane, isopentane, n-hexane, 2 methyl pentane and 5 methyl pentane.

14. The polymer according to claim 12 wherein the blowing agent is a halogenated hydrocarbon selected from symmetrical and assymetrical diehlorotetrafluoroethane and dichlorodifluoromethane.

15. The polymer according to claim l2 wherein the impregnation aid is selected from methyl chloride or monochloromonofluoromethane.

16. The polymer according to claim 15 wherein the impregnation aid is monochloromonofluoromethane. 

1. A PROCESS FOR MAKING EXPANDABLE STYRENE POLYMER PARTICLES BY CONTACTING PARTICLES OF SAID STYRENE POLYMER WITH A VOLATILE ORGANIC FLUID BLOWING AGENT, SAID BLOWING AGENT CONTAINING FROM ABOUT 0.5 TO ABOUT 20 PERCENT BY WEIGHT OF BLOWING AGENT OF AN IMPREGNATION AID CONSISTING ESSENTIALLY OF A COMPOUND HAVING A SOLUBILITY PARAMETER BETWEEN 7 AND 12 HILDEBRANDS, A CRITICAL VOLUME OF LESS THAN ABOUT 190 CM3/GRAM MOLE AND A HYDROGEN BONDING PARAMETER CONTRIBUTION TO SAID SOLUBILITY PARAMETER OF LESS THAN 5 HILDEBRANDS, THE IMPREGNATION AID BEING PRESENT IN AN AMOUNT SUFFICIENT TO PERMIT INCORPORATION OF THE BLOWING AGENT INTO THE STYRENE POLYMER PARTICLE TO FORM A FREE FLOWING STYRENE POLYMER PARTICLE.
 2. The process of claim 1 wherein the styrene polymer is insoluble in the blowing agent.
 3. The process of claim 2 wherein said styrene polymer is contacted with the blowing agent in liquid suspension.
 4. The process of claim 1 wherein the impregnation aid is selected from methyl chloride or monochloromonofluoromethane.
 5. The process of claim 4 wherein the blowing agent is a hydrocarbon selected from buTane, isobutane, pentane, isopentane, n-hexane, 2 methyl pentane and 5 methyl pentane.
 6. The process of claim 4 wherein the blowing agent is a halogenated hydrocarbon selected from symmetrical and assymetrical dichlorotetrafluoroethane and dichlorodifluoromethane.
 7. The process of claim 2 wherein the impregnation aid is monochloromonofluoromethane.
 8. The process of claim 7 wherein said styrene polymer is contacted with the blowing agent in liquid suspension.
 9. The process of claim 6 wherein the impregnation aid is selected from methyl chloride or monochloromonofluoromethane.
 10. The process of claim 1 wherein the process is performed at a temperature between about 20* and about 35* C.
 11. The process of claim 1 wherein from about 3 to about 15 weight percent of impregnation aid is used.
 12. A free flowing styrene polymer particle impregnated with a blowing agent containing from about 0.5 to about 20 percent by weight of blowing agent of an impregnation aid, said impregnation aid consisting essentially of a compound having a solubility parameter between 7 and 12 hildebrands, a critical volume of less than about 190 cm3/gram mole and a hydrogen bonding parameter contribution to said solubility parameter of less than 5 hildebrands.
 13. The polymer according to claim 12 wherein the blowing agent is a hydrocarbon selected from butane, isobutane, pentane, isopentane, n-hexane, 2 methyl pentane and 5 methyl pentane.
 14. The polymer according to claim 12 wherein the blowing agent is a halogenated hydrocarbon selected from symmetrical and assymetrical dichlorotetrafluoroethane and dichlorodifluoromethane.
 15. The polymer according to claim 12 wherein the impregnation aid is selected from methyl chloride or monochloromonofluoromethane.
 16. The polymer according to claim 15 wherein the impregnation aid is monochloromonofluoromethane. 